The present invention generally relates to a rapid thermal anneal (RTA) chamber for semiconductor wafers. More particularly, the invention relates to monitoring the reflective index of a reflector plate in-situ in a rapid thermal anneal chamber during thermal processing of semiconductors.
Rapid thermal processing (RTP) is frequently used in the semiconductor production industry in the fabrication of semiconductor integrated circuits. Such processing includes rapid thermal oxidation (RTO), which utilizes drastic and abrupt fluctuations in temperature to form a silicon oxide film on a semiconductor wafer or between layers of the wafer. One of the major advantages of using rapid thermal oxidation rather than furnace oxidation in semiconductor processing is that RTO significantly reduces the thermal budget required for transitioning between the low and high temperatures. Moreover, rapid cooling of the oxidizing chamber after a heat-induced oxidizing phase facilitates processing of a greater number of wafers per unit time, significantly enhancing semiconductor production efficiency.
RTP is important for any type of semiconductor wafer processing which requires precise temperature control and short high-temperature process intervals. Consequently, RTP must be carried out in a specially-designed rapid thermal annealing (RTA) chamber, rather than in a conventional semiconductor wafer furnace having walls and other components characterized by high thermal conductivity that would hinder rapid thermal cycling. RTA chambers are designed to thermally isolate a semiconductor wafer such that radiant, rather than conductive, heat is used in semiconductor wafer processing. As a result, all portions of the wafer are more uniformly heated, thereby eliminating or at least reducing thermal gradients which would otherwise cause wafer slip and warpage.
A typical RTA chamber includes an array of halogen, silicon-carbide or arc lamps provided in the upper portion of a sealed chamber. A cylindrical quartz tray for supporting a semiconductor wafer is rotatably mounted in a support in the bottom of the chamber, and a heat reflector plate is provided on the support inside the tray for reflecting heat from the lamps. Infrared pyrometers connected to a temperature control system absorb infrared rays reflected from the peripheral regions to the central region of the reflector plate. Conduits connected to the chamber can be utilized to distribute oxygen or other process gas over the front side of the wafer in the chamber.
During the rapid heating phase of the RTO process, a phenomenon called xe2x80x9cdopant outgassingxe2x80x9d is common, wherein dopants in the wafer, particularly if the wafer has a low backside emissivity, tend to diffuse from the backside of the wafer and are deposited onto the reflector plate. The dopant contaminants on the reflector plate cause inaccurate heat reflection to the absorptive fiber optic probes of the pyrometers, which relay faulty temperature information to the temperature control for the system. Consequently, overheating of the wafers in the chamber may occur. It is therefore very important during RTP to constantly monitor the reflective index of the reflector plate of a rapid thermal anneal chamber in order to ensure accurate and precise temperature monitoring and control of the chamber during wafer processing.
Therefore, it is an object of the present invention to ensure accurate and precise temperature control of a rapid thermal anneal chamber.
It is another object of the present invention to detect contaminants on a reflector plate of a rapid thermal anneal chamber.
It is a further object of the present invention to prevent inaccurate or imprecise thermal cycling during the processing of semiconductor wafers in a rapid thermal anneal chamber.
It is yet another object of the present invention to facilitate timely replacement of a reflector plate in a rapid thermal anneal chamber in the event of contaminant deposit on the reflector plate.
It is a still further object of the present invention to facilitate constant monitoring of a reflective index of a reflection plate in a rapid thermal anneal chamber to prevent process temperature errors in operation of the chamber.
In accordance with these and other objects and advantages, the present invention comprises one or multiple openings in the chamber wall of a rapid thermal anneal chamber and a reflective index monitor in the opening or openings, respectively. The reflective index monitor or monitors each measures the infrared reflective index of the reflector plate of the rapid thermal anneal chamber, and sends a corresponding signal to a process controller, an alarm, or both a process controller and an alarm. In the event that the measured reflective index of the reflector plate deviates from the reflective index of a control, the process controller terminates heating operation of the chamber to prevent damage to the semiconductor wafer in the chamber. The alarm may be activated to alert personnel to the need for immediate replacement of the contaminated reflector plate.